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2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4 5<book id="Linux-USB-API">
6 <bookinfo>
7 <title>The Linux-USB Host Side API</title>
8 9 <legalnotice>
10 <para>
11 This documentation is free software; you can redistribute
12 it and/or modify it under the terms of the GNU General Public
13 License as published by the Free Software Foundation; either
14 version 2 of the License, or (at your option) any later
15 version.
16 </para>
17 18 <para>
19 This program is distributed in the hope that it will be
20 useful, but WITHOUT ANY WARRANTY; without even the implied
21 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
22 See the GNU General Public License for more details.
23 </para>
24 25 <para>
26 You should have received a copy of the GNU General Public
27 License along with this program; if not, write to the Free
28 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
29 MA 02111-1307 USA
30 </para>
31 32 <para>
33 For more details see the file COPYING in the source
34 distribution of Linux.
35 </para>
36 </legalnotice>
37 </bookinfo>
38 39<toc></toc>
40 41<chapter id="intro">
42 <title>Introduction to USB on Linux</title>
43 44 <para>A Universal Serial Bus (USB) is used to connect a host,
45 such as a PC or workstation, to a number of peripheral
46 devices. USB uses a tree structure, with the host as the
47 root (the system's master), hubs as interior nodes, and
48 peripherals as leaves (and slaves).
49 Modern PCs support several such trees of USB devices, usually
50 one USB 2.0 tree (480 Mbit/sec each) with
51 a few USB 1.1 trees (12 Mbit/sec each) that are used when you
52 connect a USB 1.1 device directly to the machine's "root hub".
53 </para>
54 55 <para>That master/slave asymmetry was designed-in for a number of
56 reasons, one being ease of use. It is not physically possible to
57 assemble (legal) USB cables incorrectly: all upstream "to the host"
58 connectors are the rectangular type (matching the sockets on
59 root hubs), and all downstream connectors are the squarish type
60 (or they are built into the peripheral).
61 Also, the host software doesn't need to deal with distributed
62 auto-configuration since the pre-designated master node manages all that.
63 And finally, at the electrical level, bus protocol overhead is reduced by
64 eliminating arbitration and moving scheduling into the host software.
65 </para>
66 67 <para>USB 1.0 was announced in January 1996 and was revised
68 as USB 1.1 (with improvements in hub specification and
69 support for interrupt-out transfers) in September 1998.
70 USB 2.0 was released in April 2000, adding high-speed
71 transfers and transaction-translating hubs (used for USB 1.1
72 and 1.0 backward compatibility).
73 </para>
74 75 <para>Kernel developers added USB support to Linux early in the 2.2 kernel
76 series, shortly before 2.3 development forked. Updates from 2.3 were
77 regularly folded back into 2.2 releases, which improved reliability and
78 brought <filename>/sbin/hotplug</filename> support as well more drivers.
79 Such improvements were continued in the 2.5 kernel series, where they added
80 USB 2.0 support, improved performance, and made the host controller drivers
81 (HCDs) more consistent. They also simplified the API (to make bugs less
82 likely) and added internal "kerneldoc" documentation.
83 </para>
84 85 <para>Linux can run inside USB devices as well as on
86 the hosts that control the devices.
87 But USB device drivers running inside those peripherals
88 don't do the same things as the ones running inside hosts,
89 so they've been given a different name:
90 <emphasis>gadget drivers</emphasis>.
91 This document does not cover gadget drivers.
92 </para>
93 94 </chapter>
95 96<chapter id="host">
97 <title>USB Host-Side API Model</title>
98 99 <para>Host-side drivers for USB devices talk to the "usbcore" APIs.
100 There are two. One is intended for
101 <emphasis>general-purpose</emphasis> drivers (exposed through
102 driver frameworks), and the other is for drivers that are
103 <emphasis>part of the core</emphasis>.
104 Such core drivers include the <emphasis>hub</emphasis> driver
105 (which manages trees of USB devices) and several different kinds
106 of <emphasis>host controller drivers</emphasis>,
107 which control individual busses.
108 </para>
109 110 <para>The device model seen by USB drivers is relatively complex.
111 </para>
112 113 <itemizedlist>
114 115 <listitem><para>USB supports four kinds of data transfers
116 (control, bulk, interrupt, and isochronous). Two of them (control
117 and bulk) use bandwidth as it's available,
118 while the other two (interrupt and isochronous)
119 are scheduled to provide guaranteed bandwidth.
120 </para></listitem>
121 122 <listitem><para>The device description model includes one or more
123 "configurations" per device, only one of which is active at a time.
124 Devices that are capable of high-speed operation must also support
125 full-speed configurations, along with a way to ask about the
126 "other speed" configurations which might be used.
127 </para></listitem>
128 129 <listitem><para>Configurations have one or more "interfaces", each
130 of which may have "alternate settings". Interfaces may be
131 standardized by USB "Class" specifications, or may be specific to
132 a vendor or device.</para>
133 134 <para>USB device drivers actually bind to interfaces, not devices.
135 Think of them as "interface drivers", though you
136 may not see many devices where the distinction is important.
137 <emphasis>Most USB devices are simple, with only one configuration,
138 one interface, and one alternate setting.</emphasis>
139 </para></listitem>
140 141 <listitem><para>Interfaces have one or more "endpoints", each of
142 which supports one type and direction of data transfer such as
143 "bulk out" or "interrupt in". The entire configuration may have
144 up to sixteen endpoints in each direction, allocated as needed
145 among all the interfaces.
146 </para></listitem>
147 148 <listitem><para>Data transfer on USB is packetized; each endpoint
149 has a maximum packet size.
150 Drivers must often be aware of conventions such as flagging the end
151 of bulk transfers using "short" (including zero length) packets.
152 </para></listitem>
153 154 <listitem><para>The Linux USB API supports synchronous calls for
155 control and bulk messages.
156 It also supports asynchnous calls for all kinds of data transfer,
157 using request structures called "URBs" (USB Request Blocks).
158 </para></listitem>
159 160 </itemizedlist>
161 162 <para>Accordingly, the USB Core API exposed to device drivers
163 covers quite a lot of territory. You'll probably need to consult
164 the USB 2.0 specification, available online from www.usb.org at
165 no cost, as well as class or device specifications.
166 </para>
167 168 <para>The only host-side drivers that actually touch hardware
169 (reading/writing registers, handling IRQs, and so on) are the HCDs.
170 In theory, all HCDs provide the same functionality through the same
171 API. In practice, that's becoming more true on the 2.5 kernels,
172 but there are still differences that crop up especially with
173 fault handling. Different controllers don't necessarily report
174 the same aspects of failures, and recovery from faults (including
175 software-induced ones like unlinking an URB) isn't yet fully
176 consistent.
177 Device driver authors should make a point of doing disconnect
178 testing (while the device is active) with each different host
179 controller driver, to make sure drivers don't have bugs of
180 their own as well as to make sure they aren't relying on some
181 HCD-specific behavior.
182 (You will need external USB 1.1 and/or
183 USB 2.0 hubs to perform all those tests.)
184 </para>
185 186 </chapter>
187 188<chapter id="types"><title>USB-Standard Types</title>
189 190 <para>In <filename>&lt;linux/usb/ch9.h&gt;</filename> you will find
191 the USB data types defined in chapter 9 of the USB specification.
192 These data types are used throughout USB, and in APIs including
193 this host side API, gadget APIs, and usbfs.
194 </para>
195 196!Iinclude/linux/usb/ch9.h
197 198 </chapter>
199 200<chapter id="hostside"><title>Host-Side Data Types and Macros</title>
201 202 <para>The host side API exposes several layers to drivers, some of
203 which are more necessary than others.
204 These support lifecycle models for host side drivers
205 and devices, and support passing buffers through usbcore to
206 some HCD that performs the I/O for the device driver.
207 </para>
208 209 210!Iinclude/linux/usb.h
211 212 </chapter>
213 214 <chapter id="usbcore"><title>USB Core APIs</title>
215 216 <para>There are two basic I/O models in the USB API.
217 The most elemental one is asynchronous: drivers submit requests
218 in the form of an URB, and the URB's completion callback
219 handle the next step.
220 All USB transfer types support that model, although there
221 are special cases for control URBs (which always have setup
222 and status stages, but may not have a data stage) and
223 isochronous URBs (which allow large packets and include
224 per-packet fault reports).
225 Built on top of that is synchronous API support, where a
226 driver calls a routine that allocates one or more URBs,
227 submits them, and waits until they complete.
228 There are synchronous wrappers for single-buffer control
229 and bulk transfers (which are awkward to use in some
230 driver disconnect scenarios), and for scatterlist based
231 streaming i/o (bulk or interrupt).
232 </para>
233 234 <para>USB drivers need to provide buffers that can be
235 used for DMA, although they don't necessarily need to
236 provide the DMA mapping themselves.
237 There are APIs to use used when allocating DMA buffers,
238 which can prevent use of bounce buffers on some systems.
239 In some cases, drivers may be able to rely on 64bit DMA
240 to eliminate another kind of bounce buffer.
241 </para>
242 243!Edrivers/usb/core/urb.c
244!Edrivers/usb/core/message.c
245!Edrivers/usb/core/file.c
246!Edrivers/usb/core/driver.c
247!Edrivers/usb/core/usb.c
248!Edrivers/usb/core/hub.c
249 </chapter>
250 251 <chapter id="hcd"><title>Host Controller APIs</title>
252 253 <para>These APIs are only for use by host controller drivers,
254 most of which implement standard register interfaces such as
255 EHCI, OHCI, or UHCI.
256 UHCI was one of the first interfaces, designed by Intel and
257 also used by VIA; it doesn't do much in hardware.
258 OHCI was designed later, to have the hardware do more work
259 (bigger transfers, tracking protocol state, and so on).
260 EHCI was designed with USB 2.0; its design has features that
261 resemble OHCI (hardware does much more work) as well as
262 UHCI (some parts of ISO support, TD list processing).
263 </para>
264 265 <para>There are host controllers other than the "big three",
266 although most PCI based controllers (and a few non-PCI based
267 ones) use one of those interfaces.
268 Not all host controllers use DMA; some use PIO, and there
269 is also a simulator.
270 </para>
271 272 <para>The same basic APIs are available to drivers for all
273 those controllers.
274 For historical reasons they are in two layers:
275 <structname>struct usb_bus</structname> is a rather thin
276 layer that became available in the 2.2 kernels, while
277 <structname>struct usb_hcd</structname> is a more featureful
278 layer (available in later 2.4 kernels and in 2.5) that
279 lets HCDs share common code, to shrink driver size
280 and significantly reduce hcd-specific behaviors.
281 </para>
282 283!Edrivers/usb/core/hcd.c
284!Edrivers/usb/core/hcd-pci.c
285!Idrivers/usb/core/buffer.c
286 </chapter>
287 288 <chapter id="usbfs">
289 <title>The USB Filesystem (usbfs)</title>
290 291 <para>This chapter presents the Linux <emphasis>usbfs</emphasis>.
292 You may prefer to avoid writing new kernel code for your
293 USB driver; that's the problem that usbfs set out to solve.
294 User mode device drivers are usually packaged as applications
295 or libraries, and may use usbfs through some programming library
296 that wraps it. Such libraries include
297 <ulink url="http://libusb.sourceforge.net">libusb</ulink> 298 for C/C++, and
299 <ulink url="http://jUSB.sourceforge.net">jUSB</ulink> for Java.
300 </para>
301 302 <note><title>Unfinished</title>
303 <para>This particular documentation is incomplete,
304 especially with respect to the asynchronous mode.
305 As of kernel 2.5.66 the code and this (new) documentation
306 need to be cross-reviewed.
307 </para>
308 </note>
309 310 <para>Configure usbfs into Linux kernels by enabling the
311 <emphasis>USB filesystem</emphasis> option (CONFIG_USB_DEVICEFS),
312 and you get basic support for user mode USB device drivers.
313 Until relatively recently it was often (confusingly) called
314 <emphasis>usbdevfs</emphasis> although it wasn't solving what
315 <emphasis>devfs</emphasis> was.
316 Every USB device will appear in usbfs, regardless of whether or
317 not it has a kernel driver.
318 </para>
319 320 <sect1 id="usbfs-files">
321 <title>What files are in "usbfs"?</title>
322 323 <para>Conventionally mounted at
324 <filename>/proc/bus/usb</filename>, usbfs
325 features include:
326 <itemizedlist>
327 <listitem><para><filename>/proc/bus/usb/devices</filename>
328 ... a text file
329 showing each of the USB devices on known to the kernel,
330 and their configuration descriptors.
331 You can also poll() this to learn about new devices.
332 </para></listitem>
333 <listitem><para><filename>/proc/bus/usb/BBB/DDD</filename>
334 ... magic files
335 exposing the each device's configuration descriptors, and
336 supporting a series of ioctls for making device requests,
337 including I/O to devices. (Purely for access by programs.)
338 </para></listitem>
339 </itemizedlist>
340 </para>
341 342 <para> Each bus is given a number (BBB) based on when it was
343 enumerated; within each bus, each device is given a similar
344 number (DDD).
345 Those BBB/DDD paths are not "stable" identifiers;
346 expect them to change even if you always leave the devices
347 plugged in to the same hub port.
348 <emphasis>Don't even think of saving these in application
349 configuration files.</emphasis>
350 Stable identifiers are available, for user mode applications
351 that want to use them. HID and networking devices expose
352 these stable IDs, so that for example you can be sure that
353 you told the right UPS to power down its second server.
354 "usbfs" doesn't (yet) expose those IDs.
355 </para>
356 357 </sect1>
358 359 <sect1 id="usbfs-fstab">
360 <title>Mounting and Access Control</title>
361 362 <para>There are a number of mount options for usbfs, which will
363 be of most interest to you if you need to override the default
364 access control policy.
365 That policy is that only root may read or write device files
366 (<filename>/proc/bus/BBB/DDD</filename>) although anyone may read
367 the <filename>devices</filename>
368 or <filename>drivers</filename> files.
369 I/O requests to the device also need the CAP_SYS_RAWIO capability,
370 </para>
371 372 <para>The significance of that is that by default, all user mode
373 device drivers need super-user privileges.
374 You can change modes or ownership in a driver setup
375 when the device hotplugs, or maye just start the
376 driver right then, as a privileged server (or some activity
377 within one).
378 That's the most secure approach for multi-user systems,
379 but for single user systems ("trusted" by that user)
380 it's more convenient just to grant everyone all access
381 (using the <emphasis>devmode=0666</emphasis> option)
382 so the driver can start whenever it's needed.
383 </para>
384 385 <para>The mount options for usbfs, usable in /etc/fstab or
386 in command line invocations of <emphasis>mount</emphasis>, are:
387 388 <variablelist>
389 <varlistentry>
390 <term><emphasis>busgid</emphasis>=NNNNN</term>
391 <listitem><para>Controls the GID used for the
392 /proc/bus/usb/BBB
393 directories. (Default: 0)</para></listitem></varlistentry>
394 <varlistentry><term><emphasis>busmode</emphasis>=MMM</term>
395 <listitem><para>Controls the file mode used for the
396 /proc/bus/usb/BBB
397 directories. (Default: 0555)
398 </para></listitem></varlistentry>
399 <varlistentry><term><emphasis>busuid</emphasis>=NNNNN</term>
400 <listitem><para>Controls the UID used for the
401 /proc/bus/usb/BBB
402 directories. (Default: 0)</para></listitem></varlistentry>
403 404 <varlistentry><term><emphasis>devgid</emphasis>=NNNNN</term>
405 <listitem><para>Controls the GID used for the
406 /proc/bus/usb/BBB/DDD
407 files. (Default: 0)</para></listitem></varlistentry>
408 <varlistentry><term><emphasis>devmode</emphasis>=MMM</term>
409 <listitem><para>Controls the file mode used for the
410 /proc/bus/usb/BBB/DDD
411 files. (Default: 0644)</para></listitem></varlistentry>
412 <varlistentry><term><emphasis>devuid</emphasis>=NNNNN</term>
413 <listitem><para>Controls the UID used for the
414 /proc/bus/usb/BBB/DDD
415 files. (Default: 0)</para></listitem></varlistentry>
416 417 <varlistentry><term><emphasis>listgid</emphasis>=NNNNN</term>
418 <listitem><para>Controls the GID used for the
419 /proc/bus/usb/devices and drivers files.
420 (Default: 0)</para></listitem></varlistentry>
421 <varlistentry><term><emphasis>listmode</emphasis>=MMM</term>
422 <listitem><para>Controls the file mode used for the
423 /proc/bus/usb/devices and drivers files.
424 (Default: 0444)</para></listitem></varlistentry>
425 <varlistentry><term><emphasis>listuid</emphasis>=NNNNN</term>
426 <listitem><para>Controls the UID used for the
427 /proc/bus/usb/devices and drivers files.
428 (Default: 0)</para></listitem></varlistentry>
429 </variablelist>
430 431 </para>
432 433 <para>Note that many Linux distributions hard-wire the mount options
434 for usbfs in their init scripts, such as
435 <filename>/etc/rc.d/rc.sysinit</filename>,
436 rather than making it easy to set this per-system
437 policy in <filename>/etc/fstab</filename>.
438 </para>
439 440 </sect1>
441 442 <sect1 id="usbfs-devices">
443 <title>/proc/bus/usb/devices</title>
444 445 <para>This file is handy for status viewing tools in user
446 mode, which can scan the text format and ignore most of it.
447 More detailed device status (including class and vendor
448 status) is available from device-specific files.
449 For information about the current format of this file,
450 see the
451 <filename>Documentation/usb/proc_usb_info.txt</filename>
452 file in your Linux kernel sources.
453 </para>
454 455 <para>This file, in combination with the poll() system call, can
456 also be used to detect when devices are added or removed:
457<programlisting>int fd;
458struct pollfd pfd;
459 460fd = open("/proc/bus/usb/devices", O_RDONLY);
461pfd = { fd, POLLIN, 0 };
462for (;;) {
463 /* The first time through, this call will return immediately. */
464 poll(&amp;pfd, 1, -1);
465 466 /* To see what's changed, compare the file's previous and current
467 contents or scan the filesystem. (Scanning is more precise.) */
468}</programlisting>
469 Note that this behavior is intended to be used for informational
470 and debug purposes. It would be more appropriate to use programs
471 such as udev or HAL to initialize a device or start a user-mode
472 helper program, for instance.
473 </para>
474 </sect1>
475 476 <sect1 id="usbfs-bbbddd">
477 <title>/proc/bus/usb/BBB/DDD</title>
478 479 <para>Use these files in one of these basic ways:
480 </para>
481 482 <para><emphasis>They can be read,</emphasis>
483 producing first the device descriptor
484 (18 bytes) and then the descriptors for the current configuration.
485 See the USB 2.0 spec for details about those binary data formats.
486 You'll need to convert most multibyte values from little endian
487 format to your native host byte order, although a few of the
488 fields in the device descriptor (both of the BCD-encoded fields,
489 and the vendor and product IDs) will be byteswapped for you.
490 Note that configuration descriptors include descriptors for
491 interfaces, altsettings, endpoints, and maybe additional
492 class descriptors.
493 </para>
494 495 <para><emphasis>Perform USB operations</emphasis> using
496 <emphasis>ioctl()</emphasis> requests to make endpoint I/O
497 requests (synchronously or asynchronously) or manage
498 the device.
499 These requests need the CAP_SYS_RAWIO capability,
500 as well as filesystem access permissions.
501 Only one ioctl request can be made on one of these
502 device files at a time.
503 This means that if you are synchronously reading an endpoint
504 from one thread, you won't be able to write to a different
505 endpoint from another thread until the read completes.
506 This works for <emphasis>half duplex</emphasis> protocols,
507 but otherwise you'd use asynchronous i/o requests.
508 </para>
509 510 </sect1>
511 512 513 <sect1 id="usbfs-lifecycle">
514 <title>Life Cycle of User Mode Drivers</title>
515 516 <para>Such a driver first needs to find a device file
517 for a device it knows how to handle.
518 Maybe it was told about it because a
519 <filename>/sbin/hotplug</filename> event handling agent
520 chose that driver to handle the new device.
521 Or maybe it's an application that scans all the
522 /proc/bus/usb device files, and ignores most devices.
523 In either case, it should <function>read()</function> all
524 the descriptors from the device file,
525 and check them against what it knows how to handle.
526 It might just reject everything except a particular
527 vendor and product ID, or need a more complex policy.
528 </para>
529 530 <para>Never assume there will only be one such device
531 on the system at a time!
532 If your code can't handle more than one device at
533 a time, at least detect when there's more than one, and
534 have your users choose which device to use.
535 </para>
536 537 <para>Once your user mode driver knows what device to use,
538 it interacts with it in either of two styles.
539 The simple style is to make only control requests; some
540 devices don't need more complex interactions than those.
541 (An example might be software using vendor-specific control
542 requests for some initialization or configuration tasks,
543 with a kernel driver for the rest.)
544 </para>
545 546 <para>More likely, you need a more complex style driver:
547 one using non-control endpoints, reading or writing data
548 and claiming exclusive use of an interface.
549 <emphasis>Bulk</emphasis> transfers are easiest to use,
550 but only their sibling <emphasis>interrupt</emphasis> transfers
551 work with low speed devices.
552 Both interrupt and <emphasis>isochronous</emphasis> transfers
553 offer service guarantees because their bandwidth is reserved.
554 Such "periodic" transfers are awkward to use through usbfs,
555 unless you're using the asynchronous calls. However, interrupt
556 transfers can also be used in a synchronous "one shot" style.
557 </para>
558 559 <para>Your user-mode driver should never need to worry
560 about cleaning up request state when the device is
561 disconnected, although it should close its open file
562 descriptors as soon as it starts seeing the ENODEV
563 errors.
564 </para>
565 566 </sect1>
567 568 <sect1 id="usbfs-ioctl"><title>The ioctl() Requests</title>
569 570 <para>To use these ioctls, you need to include the following
571 headers in your userspace program:
572<programlisting>#include &lt;linux/usb.h&gt;
573#include &lt;linux/usbdevice_fs.h&gt;
574#include &lt;asm/byteorder.h&gt;</programlisting>
575 The standard USB device model requests, from "Chapter 9" of
576 the USB 2.0 specification, are automatically included from
577 the <filename>&lt;linux/usb/ch9.h&gt;</filename> header.
578 </para>
579 580 <para>Unless noted otherwise, the ioctl requests
581 described here will
582 update the modification time on the usbfs file to which
583 they are applied (unless they fail).
584 A return of zero indicates success; otherwise, a
585 standard USB error code is returned. (These are
586 documented in
587 <filename>Documentation/usb/error-codes.txt</filename>
588 in your kernel sources.)
589 </para>
590 591 <para>Each of these files multiplexes access to several
592 I/O streams, one per endpoint.
593 Each device has one control endpoint (endpoint zero)
594 which supports a limited RPC style RPC access.
595 Devices are configured
596 by khubd (in the kernel) setting a device-wide
597 <emphasis>configuration</emphasis> that affects things
598 like power consumption and basic functionality.
599 The endpoints are part of USB <emphasis>interfaces</emphasis>,
600 which may have <emphasis>altsettings</emphasis>
601 affecting things like which endpoints are available.
602 Many devices only have a single configuration and interface,
603 so drivers for them will ignore configurations and altsettings.
604 </para>
605 606 607 <sect2 id="usbfs-mgmt">
608 <title>Management/Status Requests</title>
609 610 <para>A number of usbfs requests don't deal very directly
611 with device I/O.
612 They mostly relate to device management and status.
613 These are all synchronous requests.
614 </para>
615 616 <variablelist>
617 618 <varlistentry><term>USBDEVFS_CLAIMINTERFACE</term>
619 <listitem><para>This is used to force usbfs to
620 claim a specific interface,
621 which has not previously been claimed by usbfs or any other
622 kernel driver.
623 The ioctl parameter is an integer holding the number of
624 the interface (bInterfaceNumber from descriptor).
625 </para><para>
626 Note that if your driver doesn't claim an interface
627 before trying to use one of its endpoints, and no
628 other driver has bound to it, then the interface is
629 automatically claimed by usbfs.
630 </para><para>
631 This claim will be released by a RELEASEINTERFACE ioctl,
632 or by closing the file descriptor.
633 File modification time is not updated by this request.
634 </para></listitem></varlistentry>
635 636 <varlistentry><term>USBDEVFS_CONNECTINFO</term>
637 <listitem><para>Says whether the device is lowspeed.
638 The ioctl parameter points to a structure like this:
639<programlisting>struct usbdevfs_connectinfo {
640 unsigned int devnum;
641 unsigned char slow;
642}; </programlisting>
643 File modification time is not updated by this request.
644 </para><para>
645 <emphasis>You can't tell whether a "not slow"
646 device is connected at high speed (480 MBit/sec)
647 or just full speed (12 MBit/sec).</emphasis>
648 You should know the devnum value already,
649 it's the DDD value of the device file name.
650 </para></listitem></varlistentry>
651 652 <varlistentry><term>USBDEVFS_GETDRIVER</term>
653 <listitem><para>Returns the name of the kernel driver
654 bound to a given interface (a string). Parameter
655 is a pointer to this structure, which is modified:
656<programlisting>struct usbdevfs_getdriver {
657 unsigned int interface;
658 char driver[USBDEVFS_MAXDRIVERNAME + 1];
659};</programlisting>
660 File modification time is not updated by this request.
661 </para></listitem></varlistentry>
662 663 <varlistentry><term>USBDEVFS_IOCTL</term>
664 <listitem><para>Passes a request from userspace through
665 to a kernel driver that has an ioctl entry in the
666 <emphasis>struct usb_driver</emphasis> it registered.
667<programlisting>struct usbdevfs_ioctl {
668 int ifno;
669 int ioctl_code;
670 void *data;
671};
672 673/* user mode call looks like this.
674 * 'request' becomes the driver->ioctl() 'code' parameter.
675 * the size of 'param' is encoded in 'request', and that data
676 * is copied to or from the driver->ioctl() 'buf' parameter.
677 */
678static int
679usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
680{
681 struct usbdevfs_ioctl wrapper;
682 683 wrapper.ifno = ifno;
684 wrapper.ioctl_code = request;
685 wrapper.data = param;
686 687 return ioctl (fd, USBDEVFS_IOCTL, &amp;wrapper);
688} </programlisting>
689 File modification time is not updated by this request.
690 </para><para>
691 This request lets kernel drivers talk to user mode code
692 through filesystem operations even when they don't create
693 a character or block special device.
694 It's also been used to do things like ask devices what
695 device special file should be used.
696 Two pre-defined ioctls are used
697 to disconnect and reconnect kernel drivers, so
698 that user mode code can completely manage binding
699 and configuration of devices.
700 </para></listitem></varlistentry>
701 702 <varlistentry><term>USBDEVFS_RELEASEINTERFACE</term>
703 <listitem><para>This is used to release the claim usbfs
704 made on interface, either implicitly or because of a
705 USBDEVFS_CLAIMINTERFACE call, before the file
706 descriptor is closed.
707 The ioctl parameter is an integer holding the number of
708 the interface (bInterfaceNumber from descriptor);
709 File modification time is not updated by this request.
710 </para><warning><para>
711 <emphasis>No security check is made to ensure
712 that the task which made the claim is the one
713 which is releasing it.
714 This means that user mode driver may interfere
715 other ones. </emphasis>
716 </para></warning></listitem></varlistentry>
717 718 <varlistentry><term>USBDEVFS_RESETEP</term>
719 <listitem><para>Resets the data toggle value for an endpoint
720 (bulk or interrupt) to DATA0.
721 The ioctl parameter is an integer endpoint number
722 (1 to 15, as identified in the endpoint descriptor),
723 with USB_DIR_IN added if the device's endpoint sends
724 data to the host.
725 </para><warning><para>
726 <emphasis>Avoid using this request.
727 It should probably be removed.</emphasis>
728 Using it typically means the device and driver will lose
729 toggle synchronization. If you really lost synchronization,
730 you likely need to completely handshake with the device,
731 using a request like CLEAR_HALT
732 or SET_INTERFACE.
733 </para></warning></listitem></varlistentry>
734 735 </variablelist>
736 737 </sect2>
738 739 <sect2 id="usbfs-sync">
740 <title>Synchronous I/O Support</title>
741 742 <para>Synchronous requests involve the kernel blocking
743 until the user mode request completes, either by
744 finishing successfully or by reporting an error.
745 In most cases this is the simplest way to use usbfs,
746 although as noted above it does prevent performing I/O
747 to more than one endpoint at a time.
748 </para>
749 750 <variablelist>
751 752 <varlistentry><term>USBDEVFS_BULK</term>
753 <listitem><para>Issues a bulk read or write request to the
754 device.
755 The ioctl parameter is a pointer to this structure:
756<programlisting>struct usbdevfs_bulktransfer {
757 unsigned int ep;
758 unsigned int len;
759 unsigned int timeout; /* in milliseconds */
760 void *data;
761};</programlisting>
762 </para><para>The "ep" value identifies a
763 bulk endpoint number (1 to 15, as identified in an endpoint
764 descriptor),
765 masked with USB_DIR_IN when referring to an endpoint which
766 sends data to the host from the device.
767 The length of the data buffer is identified by "len";
768 Recent kernels support requests up to about 128KBytes.
769 <emphasis>FIXME say how read length is returned,
770 and how short reads are handled.</emphasis>.
771 </para></listitem></varlistentry>
772 773 <varlistentry><term>USBDEVFS_CLEAR_HALT</term>
774 <listitem><para>Clears endpoint halt (stall) and
775 resets the endpoint toggle. This is only
776 meaningful for bulk or interrupt endpoints.
777 The ioctl parameter is an integer endpoint number
778 (1 to 15, as identified in an endpoint descriptor),
779 masked with USB_DIR_IN when referring to an endpoint which
780 sends data to the host from the device.
781 </para><para>
782 Use this on bulk or interrupt endpoints which have
783 stalled, returning <emphasis>-EPIPE</emphasis> status
784 to a data transfer request.
785 Do not issue the control request directly, since
786 that could invalidate the host's record of the
787 data toggle.
788 </para></listitem></varlistentry>
789 790 <varlistentry><term>USBDEVFS_CONTROL</term>
791 <listitem><para>Issues a control request to the device.
792 The ioctl parameter points to a structure like this:
793<programlisting>struct usbdevfs_ctrltransfer {
794 __u8 bRequestType;
795 __u8 bRequest;
796 __u16 wValue;
797 __u16 wIndex;
798 __u16 wLength;
799 __u32 timeout; /* in milliseconds */
800 void *data;
801};</programlisting>
802 </para><para>
803 The first eight bytes of this structure are the contents
804 of the SETUP packet to be sent to the device; see the
805 USB 2.0 specification for details.
806 The bRequestType value is composed by combining a
807 USB_TYPE_* value, a USB_DIR_* value, and a
808 USB_RECIP_* value (from
809 <emphasis>&lt;linux/usb.h&gt;</emphasis>).
810 If wLength is nonzero, it describes the length of the data
811 buffer, which is either written to the device
812 (USB_DIR_OUT) or read from the device (USB_DIR_IN).
813 </para><para>
814 At this writing, you can't transfer more than 4 KBytes
815 of data to or from a device; usbfs has a limit, and
816 some host controller drivers have a limit.
817 (That's not usually a problem.)
818 <emphasis>Also</emphasis> there's no way to say it's
819 not OK to get a short read back from the device.
820 </para></listitem></varlistentry>
821 822 <varlistentry><term>USBDEVFS_RESET</term>
823 <listitem><para>Does a USB level device reset.
824 The ioctl parameter is ignored.
825 After the reset, this rebinds all device interfaces.
826 File modification time is not updated by this request.
827 </para><warning><para>
828 <emphasis>Avoid using this call</emphasis>
829 until some usbcore bugs get fixed,
830 since it does not fully synchronize device, interface,
831 and driver (not just usbfs) state.
832 </para></warning></listitem></varlistentry>
833 834 <varlistentry><term>USBDEVFS_SETINTERFACE</term>
835 <listitem><para>Sets the alternate setting for an
836 interface. The ioctl parameter is a pointer to a
837 structure like this:
838<programlisting>struct usbdevfs_setinterface {
839 unsigned int interface;
840 unsigned int altsetting;
841}; </programlisting>
842 File modification time is not updated by this request.
843 </para><para>
844 Those struct members are from some interface descriptor
845 applying to the current configuration.
846 The interface number is the bInterfaceNumber value, and
847 the altsetting number is the bAlternateSetting value.
848 (This resets each endpoint in the interface.)
849 </para></listitem></varlistentry>
850 851 <varlistentry><term>USBDEVFS_SETCONFIGURATION</term>
852 <listitem><para>Issues the
853 <function>usb_set_configuration</function> call
854 for the device.
855 The parameter is an integer holding the number of
856 a configuration (bConfigurationValue from descriptor).
857 File modification time is not updated by this request.
858 </para><warning><para>
859 <emphasis>Avoid using this call</emphasis>
860 until some usbcore bugs get fixed,
861 since it does not fully synchronize device, interface,
862 and driver (not just usbfs) state.
863 </para></warning></listitem></varlistentry>
864 865 </variablelist>
866 </sect2>
867 868 <sect2 id="usbfs-async">
869 <title>Asynchronous I/O Support</title>
870 871 <para>As mentioned above, there are situations where it may be
872 important to initiate concurrent operations from user mode code.
873 This is particularly important for periodic transfers
874 (interrupt and isochronous), but it can be used for other
875 kinds of USB requests too.
876 In such cases, the asynchronous requests described here
877 are essential. Rather than submitting one request and having
878 the kernel block until it completes, the blocking is separate.
879 </para>
880 881 <para>These requests are packaged into a structure that
882 resembles the URB used by kernel device drivers.
883 (No POSIX Async I/O support here, sorry.)
884 It identifies the endpoint type (USBDEVFS_URB_TYPE_*),
885 endpoint (number, masked with USB_DIR_IN as appropriate),
886 buffer and length, and a user "context" value serving to
887 uniquely identify each request.
888 (It's usually a pointer to per-request data.)
889 Flags can modify requests (not as many as supported for
890 kernel drivers).
891 </para>
892 893 <para>Each request can specify a realtime signal number
894 (between SIGRTMIN and SIGRTMAX, inclusive) to request a
895 signal be sent when the request completes.
896 </para>
897 898 <para>When usbfs returns these urbs, the status value
899 is updated, and the buffer may have been modified.
900 Except for isochronous transfers, the actual_length is
901 updated to say how many bytes were transferred; if the
902 USBDEVFS_URB_DISABLE_SPD flag is set
903 ("short packets are not OK"), if fewer bytes were read
904 than were requested then you get an error report.
905 </para>
906 907<programlisting>struct usbdevfs_iso_packet_desc {
908 unsigned int length;
909 unsigned int actual_length;
910 unsigned int status;
911};
912 913struct usbdevfs_urb {
914 unsigned char type;
915 unsigned char endpoint;
916 int status;
917 unsigned int flags;
918 void *buffer;
919 int buffer_length;
920 int actual_length;
921 int start_frame;
922 int number_of_packets;
923 int error_count;
924 unsigned int signr;
925 void *usercontext;
926 struct usbdevfs_iso_packet_desc iso_frame_desc[];
927};</programlisting>
928 929 <para> For these asynchronous requests, the file modification
930 time reflects when the request was initiated.
931 This contrasts with their use with the synchronous requests,
932 where it reflects when requests complete.
933 </para>
934 935 <variablelist>
936 937 <varlistentry><term>USBDEVFS_DISCARDURB</term>
938 <listitem><para>
939 <emphasis>TBS</emphasis>
940 File modification time is not updated by this request.
941 </para><para>
942 </para></listitem></varlistentry>
943 944 <varlistentry><term>USBDEVFS_DISCSIGNAL</term>
945 <listitem><para>
946 <emphasis>TBS</emphasis>
947 File modification time is not updated by this request.
948 </para><para>
949 </para></listitem></varlistentry>
950 951 <varlistentry><term>USBDEVFS_REAPURB</term>
952 <listitem><para>
953 <emphasis>TBS</emphasis>
954 File modification time is not updated by this request.
955 </para><para>
956 </para></listitem></varlistentry>
957 958 <varlistentry><term>USBDEVFS_REAPURBNDELAY</term>
959 <listitem><para>
960 <emphasis>TBS</emphasis>
961 File modification time is not updated by this request.
962 </para><para>
963 </para></listitem></varlistentry>
964 965 <varlistentry><term>USBDEVFS_SUBMITURB</term>
966 <listitem><para>
967 <emphasis>TBS</emphasis>
968 </para><para>
969 </para></listitem></varlistentry>
970 971 </variablelist>
972 </sect2>
973 974 </sect1>
975 976 </chapter>
977 978</book>
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